For example, when a magnetic disk device used for reproducing and recording on hard disks and other disk recording media is used, the head placed on the front of the arm is moved to a desired position on the disk by using an arm actuator and data are recorded and reproduced.
When data are not recorded or reproduced, the head is retracted (Retract: retract) to a safe area known as a ramp so that the head does not impact the recording surface of the disk due to vibration or impact from the outside. Thus, by using the ramp to retract the head, impact of the head with the disk can be prevented. When data are recorded and reproduced, the head in the ramp is loaded to a desired position on the recording surface of the disk.
A first inclined ascending part, a horizontal, part and a second inclined descending part are disposed from a side close to the disk on the ramp. The tip of the second inclined part becomes a packing area where the head is retained.
The arm is moved by driving an actuator using, for example, a voice coil motor (VCM) or other drive means.
The abovementioned retraction must be carried out even if the power source is cut off so the voltage obtained by rectifying a back electromotive force of the spindle motor that continues to turn even after the power is cut off is used as a power source for the retraction operation.
A method is available that involves applying a constant voltage to a VCM for a prescribed amount of time during a retraction operation. This method involves a constant torque on the VCM so that acoustic noise does not result. However, since precise speed control is difficult, the actuator comes in contact with the crash stop of the end point of the ramp and is stopped at the very end of the retraction operation. As a result, the maximum value of the number of unloading operations is lowered in consideration of the reliability aspect of the impact resistance of the head.
Meanwhile, a speed control method is available that involves retracting the VCM which moves the actuator to the ramp under constant speed control while measuring the speed. When this method is used, the head moving speed can be controlled using the retraction operation and the abovementioned impact can be mitigated by reducing the speed of the head when the retraction operation has been completed.
[Patent Document 1] U.S. Pat. No. 7,301,722
Meanwhile, a voltage pulse is created in the voltage obtained by rectifying the counter electromotive force using the rotation of the spindle motor in the retraction operation when the power is cut off. When the voltage is used as is, problems exist in that VCM drive torque fluctuations occur due to the voltage pulse and this causes acoustic noise.
Taking note of this situation, an objective of the present invention is to provide a disk drive that can inhibit the occurrence of acoustic noise using a voltage pulse when retracting the head using the speed control method using the voltage obtained by rectifying the back electromotive force from the rotation of the spindle motor after the power has been cut off.